[Term Entry] Add Parkinson's Law

[AnamolR]

Description

This PR adds a new UX psychology entry titled Parkinson's Law to the uiux/concepts/ux-psychology/terms/ section.

New folder: content/uiux/concepts/ux-psychology/terms/parkinsons-law/
New images:

• media/parkinsons-law-graph-img.png
• media/parkinsons-law-comparison-img.png
  Markdown file: parkinsons-law.md includes an overview of the principle, UX-specific implications, when and how to apply it, design recommendations, and limitations.

This entry aligns with the established tone and formatting used for other psychology-based UX laws (e.g. Hicks’s Law, Fitts’s Law).

Issues Solved

Closes #6592

Type of Change

Adding a new entry

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.